Carbonless copy papers are papers which are capable of producing an image upon impact as delivered by an imaging device (typewriter, line printer, accounting machine, etc.) or by the pressure of a pen or pencil in handwritten entry. This is accomplished without the use of interleaved carbon tissue. Chemical carbonless papers function by bringing together, normally through impact or pressure, colorless components which react to produce a legible image. In most carbonless papers, the chemical reaction is similar to that of litmus paper changing color when placed in contact with an acid or alkaline solution. Proper functioning of chemical carbonless paper is dependent on some means of preventing the colorless components from meeting and reacting until this color-producing reaction is desired. The most common method of accomplishing this is through the encapsulation of one of the two components of the image-producing chemical system.
Generally, chemical carbonless papers are prepared in three configurations. The first such configuration is coated back (CB) which involves a sheet of paper with a coating of capsules (containing the color formers in an oil solution), binders and other materials on the back of the sheet. Another configuration, coated front (CF), involves a sheet of paper with a coating of color developing materials, and typically other additives, on the front of the sheet. The third configuration is coated front and back (CFB) which comprises a sheet of paper with a coating of color developers, etc., on its front surface and color forming capsules, etc., on its back surface.
Microscopic capsules, which enclose the color forming dyes, keeping them colorless until an image is formed, are what make chemical carbonless papers work. Carbonless paper manufacturers generally employ discrete capsules for isolating the color forming components from the color developers until pressure or impact breaks the capsules allowing them to react and form an image. The capsules range in size from roughly 3 microns to 15 microns, depending upon the specific system. Typically, the capsules contain an oil solution of color former in its colorless state which has the potential to become colored when released from the capsule. The chemical nature of the color former and the oil solution varies from system to system. The basic steps of encapsulation are essentially the same for all processes. These consist of emulsification of the oil solution in a suitable medium and formation of a polymeric wall around the suspended oil droplets. In some processes, it is necessary to stabilize this polymeric wall by chemical treatment. The wall material of the capsule may vary widely with gelatin, urea-formalhyde resin and nylon type materials being typical. Many other types of synthetic polymers have been used to form capsule walls.
The color formers are generally complex organic molecules which exist in an essentially colorless form, but have the capability of being readily and rapidly changed into an intensely colored form. Most color formers in use today fall into three categories according to the method of color development. The first category consists of compounds which react to mildly acid conditions to form images. The most common of these is crystal violet lacetone which produces a blue image. There are other compounds of this type which produce red, yellow, black and green images. Blends of these materials are often used to provide specific image shades. The second class of color formers functions by oxidation of the molecule for color formation. The oxidation reactions are usually very slow, and cannot be used for initial color development. Instead, they are used to provide color stability in varying degrees. The most commonly used color former of this type is penzoyl leuco methylene blue.
Color developers are substances which cause the colorless color formers to be converted to a colored form when the latter are released from their protective capsules. The color developer, of course, must be selected for a given color forming system to ensure compatability. The most common color forming systems, i.e. those which react to mildly acid conditions, employ either a phenolic resin or an acid clay as the color developer.
The coated back (CB) coatings are comprised of three essential ingredients; capsules containing the color former, cushioning material and binders. The cushioning material of the CB coating is larger in size than the microcapsules and is added to protect these capsules from inadvertent breakage and premature imaging during the processing of the carbonless paper. Cellulose (solka floc) or starch balls (non-gelatinized starch similar to anti-offset starch spray) are typical cushioning materials. Binders suitable for CB coating include such adhesives as starch and polyvinyl alcohol.
Coated front (CF) coatings contain, as the essential ingredient, the color developer. In most cases, the developer is extended by a conventional coating clay (Kaolin) for ease of application. The presence of clay necessitates a binder, usually starch and/or latex.
The separate sheets of carbonless paper are combined into a packet with the paper (from top to bottom) being set up in terms of coated back (CB), coated front and back (CFB) . . . coated front (CF) so that in each case a color former and color developer will be brought into contact when the microcapsules containing the color forming material are ruptured. A variation to the use of CB, CFB and CF paper is the self-contained (SC) carbonless paper in which both the color former and color developer materials are applied to the same side of the sheet or both incorporated into the fiber lattice of the paper sheet.
Carbonless papers are widely used in the forms industry. Typically, pre-printed forms are compiled into a packet so that marking the top form will provide the required number of duplicates. Generally, the carbonless paper is prepared in pre-collated sets in which sheets of various colors and surfaces are packaged in reverse sequence sets wherein the sheets are arranged opposite to their normal functional order. That is, the coated front sheet is first in the set and the coated back sheet last with the required number of CFB sheets in between. This is done so that when the sheets are printed, which automatically reverses their sequence in the delivery tray, they will end up in the proper functional order for subsequent data entry.
Traditionally, carbonless paper forms have been imaged by conventional printing techniques. The advent of high speed electrostatographic copiers with dependable, high capacity collating systems naturally led to attempts to print carbonless paper by this convenient imaging method. Such attempts have been problematical, however, because the base sheets upon which coatings are applied to form carbonless papers are most commonly 13 to 15 lb. basis weight sheets (17 .times. 22/500), although any weight can be utilized. The problem with using the 13, 15 or lighter weight sheets in electrostatographic copiers lies in the fact that these papers do not have sufficient stiffness (rigidity) or freedom from curl to be handled reliably in the copier's processors or sorters. One solution to this problem would be to prepare carbonless paper on heavier (ca. 20 pound) base sheets. Such sheets would possess the requisite stiffness and caliper but would present economic disadvantages. First of all, the heavier paper itself would be more expensive than that presently in use. In addition, the use of heavier paper will necessarily limit the number of sheets which can be placed in a set and still image. Of lesser importance, but still of some significance, is the fact that the use of heavier papers would necessarily increase the mailing cost of carbonless forms.
It would be desirable and it is an object of the present invention to provide a novel carbonless paper.
A further object is to provide such a paper which is suitable for reliable use in high speed electrostatographic copiers.